DE102011118295A1 - Producing an aluminum foam body, comprises providing a microporous body made of aluminum alloy reinforced with hard material particles, and melting the microporous body and then treating a melt under vacuum by acting upon with vibrations - Google Patents

Abstract

The method of producing an aluminum foam body, comprises: providing a microporous body made of aluminum alloy reinforced with hard material particles, where the aluminum alloy comprises a composition having a silicon-proportion of 15 vol.% and dissolved nitrogen; melting the microporous body and then treating a melt under vacuum by acting upon with vibrations for creating macropores by releasing the nitrogen dissolved in the aluminum alloy and expanding the micropores by the released nitrogen; and deterring the melt under maintaining a structure with macropores. The method of producing an aluminum foam body, comprises: providing a microporous body made of aluminum alloy reinforced with hard material particles, where the aluminum alloy comprises a composition having a silicon-proportion of 15 vol.% and dissolved nitrogen; melting the microporous body and then treating a melt under vacuum by acting upon with vibrations for creating macropores by releasing the nitrogen dissolved in the aluminum alloy and expanding the micropores by the released nitrogen; and deterring the melt under maintaining a structure with macropores and then maintaining the foam body. The body is formed in a stud shaped manner, where the step of providing a microporous body is carried out by spray forming of the aluminum alloy reinforced with the hard material particles under nitrogen supply. The melting step is carried out at a temperature of 720?C for 1 hour. The foam body has a density of 1.2 g/cm 3>. A melt-molding is used for the near neat shape manufacturing of foam body-components during the melting step and the deterring step. An independent claim is included for an aluminum foam body.

Description

The invention relates to a method for producing a high-strength aluminum foam body and the aluminum foam body itself.

In motor vehicle construction, metallic foams, in particular aluminum foams, which exhibit good energy absorption capacity are used, for example, as lightweight crash protection elements. In general, the use of metal foams in dynamically stressed machines offers a reduction of the mass and improvement of the dynamic stiffness and the damping properties. Other applications for metallic foams include z. As heat capsules, filters, catalyst support or sound-absorbing panels.

One common way to make a metal foam involves mixing a metal powder with a metal hydride, which is then processed into a body, usually called a "bolt", by hot pressing or extrusion molding. By heating to a temperature above the melting point of the metal gaseous hydrogen is released from the metal hydride, which foams the metal material. Alternatively, gas is blown into a molten metal to which foaming additives have been added.

These aluminum foams have a high porosity and a low density, and are deformable with the moderate specific rigidity and strength, and therefore they are used as the above-mentioned crash structures. Aluminum foams are therefore used to date in applications that require a very high strength.

Furthermore, known methods of displaying aluminum foams are not aimed at the presentation of aluminum foam products which are already close to the component shape.

Based on this prior art, it is an object of the present invention to provide a process for the preparation of metal foams, in particular of aluminum foams, which allows to produce high-strength aluminum foam body process reliable, which have a significantly higher compared to known aluminum foam body fatigue strength.

This object is achieved by a method having the features of claim 1.

Furthermore, the object of providing high-strength metal foam body, in particular aluminum foam body results.

A corresponding foam body is disclosed with the features of claim 7.

Further developments of method and component are carried out in the respective subclaims.

A first embodiment relates to a method of manufacturing a high strength aluminum foam body which first requires providing a microporous body of a hard material particle reinforced aluminum alloy having a composition having an Si content of at least 15% by volume and dissolved nitrogen , The microporous body is melted and the melt is treated under vacuum by vibratory application to produce macropores by liberating the nitrogen dissolved in the aluminum alloy and expanding the micropores by the liberated nitrogen that forms the foam structure. By a rapid quenching of the melt, the structure can be maintained with the macropores and thus the foam body can be obtained.

With the method according to the invention, it is thus possible to produce a high-strength aluminum foam body made of an AMC alloy (aluminum matrix composite), which has significantly higher strength values and thus increased fatigue strength in comparison with known foam bodies of aluminum alloys. Furthermore, with the method according to the invention, the process reliability and reproducibility in the production of a high-strength foam body of aluminum alloys is increased.

The lightweight potential of AMC alloys is extended, since their original density of 2.9 g / cm ^{3 can be} reduced by foaming to below 2 g / cm ³ , in particular to 1.2 g / cm ³ .

Advantageously, by spray compacting the aluminum alloy reinforced with hard material particles under nitrogen supply, the body, which may be formed as a bolt, and with which the melt treatment is carried out. In this way, the bolt is created with the unavoidable in the spray compaction output porosity and at the same time takes place with nitrogen as Verdüsungsgas the inclusion of nitrogen in the alloy.

The melt treatment may be carried out at a temperature in a range of 650 to 850 ° C, preferably at about 720 ° C, and the duration of vibration exposure of the melt may be in a range of about 0.5 to about 2 hours, and is preferably 1 h amount.

Suitable AMC alloys have a composition comprising 15 to 35 vol.% Si, 3 to 7 vol.% Fe, 1 to 3 vol.% Ni, 1 to 5 vol.% Mn, 0.5 to 2 vol .-% Mg, 20 to 30 vol .-% SiC _powder , and a balance Al having the usual traces of contamination.

An AMC alloy which gives particularly good properties and strength values of the foam body created therefrom has a composition of 25% by volume of Si, 5% by volume of Fe, 2% by volume of Ni, 3% by volume Mn, 1 Vol .-% Mg, 25 vol .-% SiC _powder , and the rest is Al, with the usual _{traces of} contamination on.

The AMC alloy foam body thus has high strength as well as wear resistance and high heat resistance, and thermal shock resistance, respectively. Also, the modulus of elasticity and the fatigue strength are increased in comparison to conventional aluminum foam structures.

The foam body produced can be further processed, such as cutting by sawing, milling, drilling or turning, so as to manufacture a component. In an advantageous variant, however, it is also possible with the method according to the invention to produce near-foam foam body components by using a melt mold during melting, during melt treatment and quenching which corresponds to the component contour. Such near-net shape produced foamed body components advantageously require no rework or only with very little effort.

A foamed body according to the invention, which can advantageously even be a near-net shape component, consists of a high-strength aluminum alloy reinforced with hard material particles and can be represented in particular by a method according to the invention.

The composition of the hard material particles reinforced aluminum alloy of the foam body has 15 to 35 vol.% Si, 3 to 7 vol.% Fe, 1 to 3 vol.% Ni, 1 to 5 vol.% Mn, 0.5 to 2 vol .-% Mg, 20 to 30 vol .-% SiC _powder , the rest is Al, with the usual _{traces of} contamination on. In a preferred embodiment, the composition of 25 vol .-% Si, 5 vol .-% Fe, 2 vol .-% Ni, 3 vol .-% Mn, 1 vol .-% Mg, 25 vol .-% SiC _powder The rest is Al, with the usual traces of contamination.

Due to the foam structure, the density of the foam body of the AMC alloy is less than 2 g / cm ³ , and is in particular 1.2 g / cm ³ .

These and other advantages are set forth by the following description with reference to the accompanying figures. The reference to the figures in the description is to aid in the description and understanding of the subject matter. The figures are merely a schematic representation of an embodiment of the invention.

Showing:

1 a flow chart of a method according to the invention,

2 a perspective view of a melting treatment device,

3 a micrograph of the microporosities of the aluminum alloy produced during spray compacting,

4 a micrograph of the macroporosities of the aluminum alloy produced during the melt treatment,

5 a micrograph of the microstructure of the aluminum matrix before the melt treatment,

6 a micrograph of the structure of the aluminum foam body,

7 another micrograph of the structure of the aluminum foam body.

High-strength light metal alloys for the substitution of steel or cast iron are reinforced with hard material particles. In general, composites of hard material particles in a metallic matrix are referred to as MMC alloys (metal matrix composite); if the metallic matrix is an aluminum alloy, these are referred to as AMC alloys (aluminum matrix composite). As hard material particles often silicon carbide or corundum are used with a share of up to 20 percent.

The use of AMC alloys in combination with the spray compaction of the AMC alloy is already known for the production of friction rings for a brake disk and is used, for example, in US Pat DE 10 2009 049 875 A1 and the DE 10 2009 059 806 A1 described. It also describes the production of a hollow cylindrical semi-finished product for the friction rings by means of spray compacting the AMC alloy. However, no foam is produced there.

The invention, however, relates to a melting process for producing a high strength aluminum foam body from an AMC alloy. The hard material particles, which are predominantly ceramic particles, may be SiC, Al ₂ O ₃ , TiO ₂ , B ₄ C or diamond. According to the invention, a spray-compacted AMC alloy is used as the starting material, thereby creating the conditions for the production of the foam body. The method steps according to the invention are in 1 outlined.

The starting material, a SiC particle-reinforced spray-compacted aluminum alloy, is placed in a melt mold and heated in a heating device, e.g. As a furnace, heated under vacuum very quickly to a temperature above the melting temperature and treated for a certain period of time at this temperature level. In this case, vibrations are introduced into the melt. 2 shows a device in which the melt mold 1 on a vibration table 2 is arranged, which conducts appropriate mechanical vibrations in the melt. In addition, the device has horizontal vibrators 3 on, which initiate further vibrations in other directions in the melt. Of course, further devices for introducing vibrations into the melt are conceivable, for example ultrasound transmitters.

After treatment in the oven, the melt mold is removed and immediately quenched. The quenching can be carried out by means of water or oil with or without additives in a conventional manner. Fast quenching is important in order to produce a "freezing effect" or to maintain the microstructure produced during the melt treatment without reorganization reactions.

The solidus and liquid temperature of spray-compacted aluminum alloys of this type are at about 550 ° C and 620 ° C, which is slightly higher than the non-reinforced conventional aluminum alloys. For the melt treatment therefore higher temperatures are needed. With a melting temperature of about 720 ° C, the desired microstructure can be produced reliably.

Spray compaction can be used to realize a composition of the AMC alloy used which minimizes or even precludes unwanted chemical reactions at such high temperatures between the aluminum matrix alloy and the ceramic hard material particles. In general, chemical reactions such as (4Al + 3SiC → Al4C3 + 3Si) or (4Al + 4SiC → Al4SiC4 + 3Si) are to be expected in the melt at such high treatment temperatures and corresponding treatment times. These reactions may be advantageous when using a spray-compacted AMC alloy be prevented because these reaction products unfavorably make the material very brittle and very sensitive to hydrogen corrosion.

A preferred composition of the spray-compacted AMC alloy used is: material volume fraction al balance Si 25% Fe 5% Ni 2% Mn 3% mg 1% SiC _powder 25%

The main advantage of the selected alloy is the high Si content, which is here at 25%, which is not feasible casting technology but only available by spray compacting, since the eutectic range of aluminum alloys produced by casting technology is about 13% and a maximum of 14%. Thus, spray-compacted Al alloys, due to the manufacturing process, can have high Si contents of 15 to 35% to improve wear resistance, while high levels of Fe, Ni, Co, and the like. a. ensure good heat resistance.

In spray compacting, a process technology to be located between melt metallurgy and powder metallurgy, a liquid metal stream is sprayed through a nozzle with the aid of an inert gas and the fine metal drops are spun onto a turntable at a high spray speed where they are captured and compacted into a stud. Depending on the spraying parameters, microporosities are formed in the bolt, which are eliminated in the usual use of spray-compacted semi-finished products by extrusion or isostatic hot pressing (HIP) in order to obtain a compacted material.

Nitrogen is preferably used as the atomizing gas, which diffuses into the spray-compacted alloy, dissolves in the alloy in a certain amount during spraying, and is partly also entrapped as micropores in the sprayed material.

Thus, an uncompressed spray-compacted AMC alloy is used for the process according to the invention, in which therefore microporosities are present, see photographs in ( 3 . 4 ) which show various magnifications of a treated alloy or different magnifications of porosities before and after treatment produced during spraying.

5 shows a microstructure of the aluminum matrix before the melt treatment. Further, the uncompressed spray compacting alloy contains a certain amount of dissolved nitrogen in a diffused state. During the melt treatment according to the invention, these microporosities produced in the spraying process and the diffused nitrogen are utilized to produce the highly porous foam body.

The high proportion of silicon in the AMC alloy is used in the inventive melt treatment to exclude the chemical reaction between aluminum and SiC. In addition to the fact that this reaction is suppressed by the high Si content, the critical reaction temperature and reaction times can be significantly increased, for example to 850 ° C and 2 h treatment time.

This opens up the possibility of treating the melt from the spray-compacted AMC alloy, for example at a temperature of 720 ° C. for 1 h, in accordance with the novel melt treatment in which the porosities of the foam body are produced.

After melting the AMC alloy at 720 ° C, the existing microporous sites are replenished by the nitrogen released from the alloy. During treatment under mechanical vibrations, the microporosities are inflated by the released gaseous nitrogen. The formed macroporosity is in the uptake of 4 to see. If the melt in the melt mold is quenched very quickly, the formed microstructure solidifies with the generated porosity.

Thus, the highly porous foam body is obtained from an AMC alloy whose structure in the in 6 shown recording is seen.

The AMC alloy foam body according to the invention has mechanical properties in terms of strength and wear resistance, which are significantly better than the conventional aluminum foam body.

For a foam body according to the invention, the following mechanical values were determined: property value R _m MPa 420 R _p0,2 MPa 259 Modulus GPa 136 hardness HB 480 or 900 (SiC sites) A5 % 1.9

Thus, the foam body produced according to the invention has very high mechanical strength values.

Further increase the silicon primary crystals generated in the melt treatment and the intermetallic phases such. As Al ₃ Si ₂ Fe and Al ₄ SiFeNi the matrix and wear resistance of the alloy clearly.

On the basis of in 6 The microstructure shown illustrates the formation of the intermetallic phases, which significantly increase the strength of the aluminum matrix in the foam body. The dark gray areas A are silicon-prism crystals for which a hardness of about 1100 HV was determined. B shows in a range of fine-grained matrix AlSi13 in eutectic phase with about 70 HV. The gray Al3Si2Fe phases C have a hardness of about 700 HV, while the black SiC sites D have a hardness of about 2500 HV and the light gray Al4SiFeNi phases E of about 600 HV.

The inventive melt treatment process for producing a component from a high-strength aluminum foam is inexpensive and reliable. The foam body has a low density of 1.2 g / cm ³ and thus has great lightweight potential. At the same time, it has a very high modulus of elasticity, high strength and wear resistance due to the SiC reinforcement and high thermal resistance due to the high Si, Ni and Fe content in the microstructure.

Furthermore, the foam body has a high damping capacity and shows chemical stability even under high thermal stresses by Mg and Mn additives in the aluminum matrix. The foam body has by the method of manufacture no open pores but only closed pores, which contributes to an extremely low susceptibility to corrosion and highest operational stability.

By using a melt mold, which allows the near-net shape production of components, many geometrical degrees of freedom result for the preparation of the components.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009049875 A1 [0033]
• DE 102009059806 A1 [0033]

Claims (10)

A method of making a high strength aluminum foam body comprising the steps of: Providing a microporous body of a hard material particle reinforced aluminum alloy having a composition with an Si content of at least 15% by volume and dissolved nitrogen, Melting of the microporous body and treatment of the melt under vacuum by applying vibrations, thereby generating macropores by releasing nitrogen dissolved in the aluminum alloy and expanding the micropores by the liberated nitrogen, Quenching the melt while maintaining the microporous microstructure and obtaining the foam body. The method of claim 1, wherein the providing of the body, which in particular has a stud shape, is carried out by spray compacting the hard material particles reinforced aluminum alloy under nitrogen supply. Method according to claim 1 or 2, in which the melt treatment is carried out at a temperature in a range of 650 to 850 ° C, preferably at about 720 ° C, and a duration of vibration exposure of the melt is in a range of about 0.5 to about 2 hours, preferably 1 hour. Method according to at least one of claims 1 to 3, wherein the aluminum alloy reinforced with hard material particles has a composition of 15 to 35 vol.% Si, 3 to 7 vol.% Fe, 1 to 3 vol.% Ni, 1 to 5 vol % _By weight of Mn, 0.5 to 2% by volume of Mg, 20 to 30% by volume of SiC _powder balance Al having usual traces of contamination and in particular a composition of 25% by volume Si, 5% by volume Fe, 2% by volume of Ni, 3% by volume of Mn, 1% by volume of Mg, 25% by volume of SiC _powder , balance Al, with customary impurity traces. Method according to at least one of claims 1 to 4, wherein the foam body has a density of less than 2 g / cm ³ , in particular 1.2 g / cm ³ . Method according to at least one of claims 1 to 5, wherein in melting, in the melt treatment and the quenching a melt mold is used for near-net shape production of a foam body component. Aluminum foam body, characterized in that the aluminum foam body consists of a high-strength reinforced with hard particles aluminum alloy, and in particular by a method according to at least one of claims 1 to 6 can be produced. Aluminum foam body according to claim 7, characterized in that the aluminum alloy reinforced with hard material particles has a composition of 15 to 35% by volume of Si, 3 to 7% by volume of Fe, 1 to 3% by volume of Ni, 1 to 5% by volume. % Mn, 0.5 to 2 vol% Mg, 20 to 30 vol .-% SiC _powder , balance Al, having common traces of contamination, and in particular a composition of 25 vol .-% Si, 5 vol .-% Fe, 2 vol .-% Ni, 3 vol .-% Mn , 1 vol .-% Mg, 25 vol .-% SiC _powder balance Al, having conventional traces of contamination. Aluminum foam body according to claim 7 or 8, characterized in that the density of the foam body is less than 2 g / cm ³ , in particular 1.2 g / cm ³ . Aluminum foam body according to at least one of claims 7 to 9, characterized in that the aluminum foam body is a near-net shape component.

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